This is the theme that plays during the Barrel Cannon minigame for Fungi Forest, but the melody has been replaced with the overworld theme from Super Mario Bros. Both songs feature three part harmonies, and the first two notes line up perfectly with the DK64 song. It also just happened to work out that the stage is called Fungi Forest, and mushrooms play a huge part in the Super Mario series. Also, as was common with a lot of my early rips, when the song fades out, the Nutshack theme is present.